Hi my dear family and friends sailors. Yesterday did a test on my Tasman 26 with reconditioned yse8 and a bit over pitched prop 3 blades 10.5x11 (it was impossible to make it smaller due to the model) Hull is clean. Prop is prop speeded. On 900 revs speed is 3 knots consumption is next to nothing, 1200 revs boat is going 4 knots and consumes 0.7 l per hour. On 2500 revs boat is pushing 5.7 knots and drinks almost 2L per hour.
double revs, 300% increase in diesel consumption but speed is only 35% up.
Really not worth pushing that engine to the max, it start to smoke due to over pitched propeller. The sweetest spot is 2000 revs 5 knots of speed and consumption is about 1L per h.if outside of the heads looks ugly, otherwise 1200 revs and happy days. amazing amount of power (torque) on 1200 revs while engine is so quite and consumption is next to nothing.
With 30L of diesel I could motor for 40 hours and reach 160nm on 1200 revs. That is impressive.
Select to expand quoteJolene said..
1 lt per 5 nautical miles,,, awesome !!!
Yes, the boat is light and small.. just imagine 45 footer boat ????????
39ft with 39hp Yanmar gives about 1.8 litres per hr at 5kn / 1800 rpm. A few thousand hrs on the clock but very well maintained and clean bum.
Standard passage planning equation (except for very small diesels) is the formula
1 litre per hour per 10 horsepower used.
So 39hp at 1800 rpm is producing about 18hp to push at 5 knots (you can check this in the engine manual.) hence 1.8 l/hr
Even works for twins, twin 120s is 240 but at ocean cruise at 8.3 needs about 160hp which is 16l/hr
always explains why one of the most important things to get relight is prop efficiency.
that said on very light race boats often best to overpitch slighter to get the engine to work harder.
